Motor nerves interact with skeletal muscles in a relationship which is termed "trophic." The neurotrophic influences not only maintain the integrity of the muscles, but also determine some of their specific metabolic and physiological properties. The major purpose of the proposed project is to continue and extend our analysis of this trophic relationship, particularly with regard to the contributions of cholinergic transmission and muscle usage. We will assess the ability of electrical and chemical (cholinergic) stimulation of muscle to substitute for neurotrophic influences. We will continue to study the effects of disuse, and of blockade of cholinergic transmission on certain exceptional properties of muscle. In addition the effects on muscle of nutritional deprivation will be studied. It is anticipated that this work will lead to a clearer understanding of the development of muscle, and of the trophic influences of nerve on muscle.